pressure problem

[Paul]

My sand filter is gaining about 10-12psi in a short period of time in the filter position. This causes the flow of water into the pool to become very weak. During the backwash cycle it starts out flowing strong and shortly the flow of water decreases and then turbulence is seen in the pump basket. I have been struggling with this problem since the middle of last summer excluding the winter months. I have tried filter cleaners, even changed the sand and the standpipe and laterals out last summer. I am at my whits end. A water leak developed enough this summer to flow out from under the concrete deck around the pool. I have had the concrete removed and found a crack in an elbow and have repaired the pipe. I was hoping that was going to solve the water flow and pressure problem but it did not. I would greatly appreciate any help.